The disclosure of Japanese Patent Application No. 2000-048516 filed on Feb. 25, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates in general to a power output apparatus and a control method of the apparatus, and more particularly to a power output apparatus that is capable of generating power at least from an electric motor to a drive shaft, and a control method of the apparatus.
2. Description of Related Art
A known example of the above type of power output apparatus is disclosed in Japanese Patent Laid-Open Publication No. HEI 9-58295. The disclosed power output apparatus provides two or more torque patterns of an electric motor, from which one torque pattern is selected for driving the electric motor in a controlled manner. The power output apparatus is constructed such that power can be generated from an internal combustion engine and the electric motor to the drive shaft. The electric motor is operable to produce torque when the torque produced by the engine is insufficient, so as to achieve a currently required torque. More specifically, the power output apparatus stores two or more torque patterns, each of which indicates the output torque of the electric motor in percentage in relation to the accelerator position (i.e., an operation amount of the accelerator pedal), and drives the electric motor in a controlled manner by selecting one of the torque patterns.
However, the known power output apparatus does not take account of matching or balance between the output characteristics of the engine and those of the electric motor, and thus may not be able to exhibit appropriate or desired output characteristics. In particular, the known apparatus does not take energy efficiency into consideration, and therefore may exhibit poor energy efficiency depending upon the selected pattern.
It is an object of the invention to provide a power output apparatus capable of changing its output characteristics, and a control method thereof.
It is another object of the invention to provide a power output apparatus that assures enhanced driveability experienced by the driver, and a control method thereof.
It is yet another object of the invention to provide a power output apparatus that exhibits improved energy efficiency, and a control method thereof.
To accomplish the above and other objects, a first aspect of the present invention provides a power output apparatus operable to generate power from at least an electric motor to a drive shaft, which includes a pattern storing unit, a pattern selecting unit and a drive controller. The pattern storing unit stores a plurality of output characteristic patterns in which power is generated to the drive shaft, and a pattern selecting unit selects one of the output characteristic patterns stored in the pattern storing unit. The drive controller controls driving of at least the electric motor so that power that is within a range of the selected output characteristic pattern is generated to the drive shaft.
In the power output apparatus according to the first aspect of the invention, when the pattern selecting unit selects one from the plurality of output characteristic patterns of power generated to the drive shaft, the drive controller is operable to control driving of at least the electric motor so that power, as represented by the selected output characteristic pattern, is generated to the drive shaft. This makes it possible to cause the power output apparatus to generate power using a desired output characteristic pattern, thus assuring improved driveability experienced by the operator.
The power output apparatus according to the first aspect of the invention may further include an internal combustion engine operable to generate additional power to the drive shaft. In this case, the above-indicated drive controller controls driving of both the electric motor and the engine. Thus, the power as represented by the selected output characteristic pattern can be generated by controlling driving of the electric motor and the engine.
According to a second aspect of the invention, there is provided a power output apparatus operable to generate power from at least an electric motor to a drive shaft, which includes a command generating unit and a drive controller. The command generating unit generates a command to drive the electric motor with a driving characteristic that exceeds a rated value of the driving characteristic of the electric motor, and the drive controller controls driving of the electric motor. The drive controller is operable, in response to the command from the command generating unit, to control driving of the electric motor with the driving characteristic that exceeds the rated value for a limited period of time.
In the apparatus according to the second aspect of the invention, when a command to drive the electric motor with a driving characteristic that exceeds its rated value is generated, the drive controller operates to drive the motor with the driving characteristic exceeding the rated value, but for a limited period of time. Thus, the apparatus makes further use of the performance of the electric motor.
According to a third aspect of the invention, there is provided a control method of a power output apparatus operable to generate power from at least an electric motor to a drive shaft, comprising the steps of: (a) selecting one from a plurality of output characteristic patterns in which power is generated to the drive shaft; and (b) controlling driving of at least the electric motor so that power that is within a range of the selected output characteristic pattern is generated to the drive shaft. This control method makes it possible to generate power from the power output apparatus, using a desired output characteristic pattern, thus assuring improved driveability experienced by the operator.
According to a fourth aspect of the invention, there is provided a control method of a power output apparatus operable to generate power from at least an electric motor to a drive shaft, comprising the steps of: (a) generating a command to drive the electric motor with a driving characteristic that exceeds a rated value of the driving characteristic of the electric motor; and (b) controlling, in response to the command, driving of the electric motor with the driving characteristic that exceeds the rated value for a limited period of time. With this method, the power output apparatus is able to make further use of the performance of the electric motor.